Process for separating alkyl phenols



Aug. 17, 1943. D. B ,LUrr-EN, JR., ETAL 2,327,312

PROCESS FOR SEPRATING ALKYL PHENOLS Filed July 15, 1941 5 Sheets-Sheet 1 Phenolic Fracron lnvenwrs'. Danielf B. Lui'en Jr. Mdo De Benedds Aug. 17, 1943. D. B. LUTEN, JR., Erm. 2,327,312

PROCESS FOR SEPARATING ALKYL PHENOLS 3 Sheets-Sheml 2 Filed July l5, 1941 'Aug' 17, 1943- D. B. LUTEN, JR., rsru.` 2,327,312

PROCESS FOR SEPARATING ALKYL PHENOLS 3 Sheets-Sheet 5 Filed July 15, 1941 aient Ang, i?,

.UNirsD rno'cnss Fon ci Delaware pursues nay i5, wir, sensi Ni. mais@ (ci. acc-sen 2 Claims.

The present invention relates to a process for the separation oi allryl phenols. More particularly it relates to a process wherein mixtures of alkyl phenols are sulfonated to form sulfonic acids which are selectively decomposed and separated. v

in the past it has been proposed. to separate mixtures of alliyl phenols by the so-called Briclrner process, in which a mixture of these compounds is treated with sulfuric acid under conditions to form allryl phenol mono-sulionic acids. The acids so formed are diluted with Water and the .resulting mixture is steam distilled. As the sulionic acids hydrolyze to regenerate the original phenols, the latter are vaporized with the steam and pass overhead. those alkyl phenols which decompose most readily pass overhead first, while the more stable phenols pass overhead only after the mixture is allowed to come to a yhigher temperature for the hydrolysis of the corresponding sulfonlc acids. This temperature is regulated by controlling the amount of water in the boiling nun tofore required. Still further objects will become apparent from reading the following speclocation.

Our invention comprisessubjecting a mixture of alkyl phenols to the action of sulfuric acid or other sulfonating agent,` such as chlorsulfonic acid, etc., under conditions to form predominantly monosulfonic acids with phenols, and separating the monosulfonic acids formed from free phenols with the aid of a. stable waterimmiscible solvent in which the sulfonic acids and the phenols are soluble. We may operate in such a. manner that substantially all of the phenols are monosulfonated, or we may prefer to sulfonate only a portion of the phenols in the original mixture to form monosulfonic acids. In the former case we fractionally hydrolyze the resulting totally sulfonated product, preferably in the presence of a stable water-immiscible solvent for phenols, which may later be used in separating phenols from residual monosulfonic acids. In case We operate to sulfonate only a portion ofthe phenols, we prefer to separate the sulfonatd phenols from any uri-suitomated residue by means of solvent prior to hydrolysis, partial or otherwise, of the phenol monosulfonic acids.

ln cases where we sulfonate substantially all of the initialvmixture, our process usually involves the following steps: (l) sulionating the mixture; (2) diluting the reaction mixture so formed with water, and preferably adding solvent; (3) maintaining the resulting reaction mixture at conditions oi acidity, concentration and temperature favorable to hydrolysis until the optimum amount of least stable sulfonic acids has hydrolyzed; (e) subjecting the reaction mixture containintf free phenols and unhydrolyzed sulfonlc acids to extraction with or garlic solvent to produce a first phenolic frac-- tion and residual unhydrolyzed sulionic acids; (5) adjusting the conditions to iavor further hydrolysis of the residual mixture by the ad justmen't of Water and/or acid concentration and/or increasing the temperature of the mixture, etc., to effect further hydrolysis of the residual portion of the sulfonic acids; and (6) subjecting the resulting mixture containing a second quantity of free phenols to a second solvent extraction With an organic solvent to remove the second quantity of phenols and repeating the above operation until the desired number of phenolic fractions has been separated.

In cases where we operate to sulfonate onli7 a portion of the intial mixturethe steps are generally as follows: (l) the mixture is partially sulfonated; (2) the resulting product, preferably in the presence of water, is treated with solvent .to separate free phenols to produce a. solvent phase containing dissolved free phenols and a residual monosulonic acid-phase as a first product; (3) the solvent is separated from said free phenols; (4) said free phenols are further partially sulfonated; (5) the resulting mixture is treated with solvent to produce a second residual sulfonic acid layer as a second product and a solvent layer containing phenols; and (6) the above steps are repeated until the desired number of sulfonic acid fractions has been produced. The sulfonic acid fractions are hydrolyzed to regenerate the corresponding free phenols.

Our separation depends upon the different tendencies toward hydrolysis which the various alkyl phenol sulfonic acids exhibit under different conditions for hydrolysis, as well as their tendencies to be sulfonated at different rates under dlerent conditions of -sulfonation This latter will be discussed at length hereinafter. 'I'his tendency to hydrolyze depends upon a number of factors, the more important of which are the structure of the alkyl phenol sulfonic acid, the temperature, and the nature of the hydrolytic medium. This latter is a complex function of the concentration of acid, the concentration of water, the amount of undissociated sulfonic acid present, the dielectric properties of the medium, etc. Also, a given temperature increase may increase the velocity of hydrolysis more for one sulfonic acid than another. We have found that, in general, for any given alkyl phenol sulfonic acid there exists an optimum set of conditions for hydrolysis. Our invention is based upon the maintenance of the sulfonic acid mixture under conditions of hydrolysis such that principally only one or a particular group of sulfonic acids hydrolyzes, then separating the corresponding alkyl phenol, changing the hydrolytic conditions of the residual unhydrolzed sulfonic acids to favor the hydrolysis of some other sulfonic acid or group of acids, separating these and continuing as above until the'desired degree of separation is attained.

We have found that the most convenient way to adjust the hydrolytic conditions is to vary the temperature and the acid concentration of the .mixture to be hydrolyzed, the latter factor including adjusting the concentration of the sulfonic acids themselves.' 'I'his is accomplished by carrying out the hydrolysis in vessels in which the heat input can be controlled, as by steam coils, jacketing and the like, and by adjusting the acid concentration of the .mixture by the addition and/or evaporation of Water or the addition of acid.

Our invention can be better understood from the figures, which,represent different embodiments thereof.

Figure I is a flow diagram representing the batch method for carryingv out our process. Agitator I is a vessel equipped with stirrer 2 run by motor 3, and heating coil 4, as well as offtake manifold comprising valves 5 to I9, is adapted to stand elevated pressures and is provided with safety valve II.

In the iirst stage of operation, valves 5-I II and I2 are closed and valves I3 and I4 are opened, charging agitator I with the proper quantities of alkyl phenols and sulfuric acid, respectively. Stirrer 2 is started and the sulfonation allowed to proceed until substantially all of the phenols have been sulfonated. If desired, this reaction rate may be increased or the type of sulfonation altered, as explained below, by increasing the temperature by means of coil 4.v

When the phenols are sulfonated to the desired degree, the conditions for partial hydrolysis of the sulfonic acids are adjustedas desired by admitting sulfuric acid and/or water by valves I4 and I5, respectively. A substantially water-imrniscible solvent for phenols, such as benzene, is run into agitator I via valve I6 for the reasons discussed below. The temperature is regulated by means of coil 4 for optimum hydrolysis. When the sulfonic acids have hydrolyzed to the desired degree and the system has come to equilibrium with respect to the solvent, stirrer 2 is stopped and the mixture allowed to separate into two phases, an upper solvent phase containing dissolved phenols and a lower aqueous phase containing sulfuric acid and unhydrolyzed sulfonic acids. Valve I'I is closed and the upper solvent phase is withdrawn through the proper valve in asazsiz be Withdrawn through the proper valve of the manifold system and allowed to pass to tank I9.

Then the extraction may be repeated until the required degree of separation of free phenols from sulfonic acids is attained. After the separation of two Aphases after the addition of the last portion of solvent, valves 20, 2| and 22 are closed and valves I2 and 23 are opened allowing the bottom phase to pass through line 2'4 to sulfonic acid storage tank 29.

If desired, the acidity of the residual unhydrolyzed sulfonic acid can be increased by closing valve 23 and passing the lower phase through evaporator 25 equipped with heating coil 26. A portion of water may then be evaporated, passing out through line 21. After sufficient water has been evaporated, valve 28 is opened and the A.concentrated sulfonic acid solution is passed through line 24 to tank 29.

When all of the lower phase has passed from agitator I, valves 2| and 23 are closed and valves I2 and 20 are opened. This admits the last solvent portion to tank I9. The solvent and phenols are passedl from tank I9 through valve Il to distillation column I8 equipped with reboiler 30 and partial condenser 3 I. In column IB the solvent is separated from the phenols which latter are withdrawn from the bottom of still 21 through valve 32 and passed to storage not shown, while solvent passes off the top of still I8 through line 33 to condenser 34, thence to solvent tank 35 for use in another cycle.

In stage II the cycle is repeated further separating the unhydrolyzed sulfonic acids. Valve 36 is opened and sulfonic acids from tank 29 are charged toA agitator I. The acidity of the mixture in agitator I is adjusted by the addition of acid and/or water through valves I4 and I5, respectively. In this hydrolysis, the conditions are adjusted to favor the hydrolysis of a second portion of the residual unhydrolyzed sulfonic acids to form a second phenolic fraction. The above cycle is then repeated and the still more diiilcultly hydrolyzable sulfonic acids hydrolyzed until the required number of phenolic fractions has been separated. At the end of the process sulfuric acid may be withdrawn from the system through draw-olf valve 22.

Figure II is a flow diagram representing a continous method for carrying out our process. Sulfuric acid and alkyl phenols are continuously admitted to reactor 50 wherein monosulfonic acids are formed which feed continuously hydrolyzer 5I to which water and preferably a portion of solvent areA admitted. The mixture leaving hydrolyzer 5I contains sulfonic acids and unhydrolyzed phenols, which pass to extractor 52, wherein they are contacted with a further quantity of solvent. The solvent selectively dissolves the phenols and the extract phase so formed passes to distillation column 53 wherein phenol fraction #1 is separated from solvent, which latter is returned for use in another cycle. The rafiinate containing unhydrolyzed sulfonic acids Passes to evaporator 54 wherein the acidity of the solution is increased. From evaporator 54 the mixture passes to hydrolyzer 55 to which preferably a portion of solvent may be added and also sulfuric acid. The increased acidity affects the equilibwith 50 cc. of benzene. The benzene extracts, which contained only traces of sulfonic acids,

were washed with a dilute solution of sodium bi;

carbonate and then distilled to recover the alkyl phenols contained in them. These were found to amount to about 25% oi' the charge and contained so much 2,4,6-trimethyl phenol that considerable amounts of it crystallized from the liquid at room temperature. The 2,4,6-trimethyl phenol recovered upon ltration of the mixture amountedto 25 grams.

Example II were washed with sodium bicarbonate solution' to remove the traces of sulfonic acids present, following which thebenzene was distilled oif and the alkyl phenols recovered. Upon fractional distillation of these unsulfonated phenols a fraction, amounting to 50 grams, which contained 32% of 2,3,5-trimethy1 phenol, was recovered. The 2,3,5-trimethy1 phenol precipitated out of this mixture at room temperature and grams 0f the pure substance was recovered by filtering.

Another portion of the original mixture was subjected to a. fractional distillation under conditions similar to those' employed with the unsuifonated fraction. However, under these conditions it was not possible to obtain a fraction which contained a suiicient concentration of 2,3,5- trimethyl phenol to cause any of that substance to precipitate out of solution.

Example III A mixture containing 100 grams of 2,5-dimethyl phenol sulfonic acid and 100 grams of 2,6-dimethyl phenol sulfonic acid in solution in 300 grams of 50% sulfuric acid was heated at 100 C. for 20 hours. At the end of this period, the reaction mixture was cooled and extracted with a portion of toluene. The toluene was washed with sodium bicarbonate solution to remove traces of sulfuric acid and sulfonic acid and then distilled off to leave a residue of about 50 grams of almost pure 2,5-dimethyl phenol. Since the hydrolysis of 2,6-dimethyl phenol sulfonic acid in 50% sulfuric acid is very slow at 100 C., the temperature of *the residual liquid was raised to 125 C. for an additional ten hours. At the end of this period, the reaction mixture was cooled and extracted with toluene. Following the usual washing of the extract phase, the toluene was distilled off to leave a residue of 60 grams of l80% pure 2,6-dimethyl phenol.

It is clear that if the first period of heating had been some what longer then the 2,5-dimethyl phenol recovery would have been larger, but its purity would have been less; there would be an accompanying diminution in yield and increase in purity of the 2,6-dimethyl phenol. Actually, while such modifications of the process could be carried to absurdity, an addition of ten hours to the first period of hydrolysis would have increased the yield of 2,5-dimethyl phenol to about 58 grams and would have resulted in the simultaneous hydrolysis of only about 2 grams more of 2,6-dimethyl phenol.

Example IV A mixture of grams of 2,4-dimethyl phenol sulfonic acid and 100 grams of 2,5-dimethyl phenol sulfonic acid in solution in 300 grams of 50% aqueous sulfuric acid was heated at 100 C. for three hours. At the end of this period, the reaction mixture was extracted with toluene and the toluene phase washed to remove small amounts of sulfuric and sulfonic acids. The alkyl phenols which were recovered by distillation of the extract phase amounted to 50 grams and contained 75% of 2,4-dimethyl phenol. If the hydrolysis were carried out at -lower temperatures, the separation would be even better, although the time required would be much longer. At higher temperatures, the separation is poorer and, in the neighborhood of -125" C., the relative rates of hydrolysis are reversed, the 2,5- oimethyl phenol sulfonic acid being more rapidly hydrolyzed than the 2,4-dimethyl phenol sulfonic acid. v

We claim as our invention:

l. A process for separating a mixture of alkyl phenols comprising the steps of sulfonating said mixture under conditions to favor monosulfonation, adding water and a, substantially waterimmisicible solvent to the resulting alkyl phenol monosulfonic acids, maintaining the resulting mixture under conditions favorable to hydrolysis until a part of said sulfonic acids has hydrolyzed, then extracting the resulting mixture with /said solvent to form a solvent phase containing dissolved alkyl phenols and a residual phase containing alkyl phenol monosulfonic acids, and subsequently hydrolyzing the residual sulfonic acids to regenerate the corresponding phenols.

2. The process of claim 1 wherein thesulfonation is carried out at a temperature between about 0 C. and 150 C. with sulfuric acid in an amount of from about one to 5 equivalents of sulfuricracid per equivalent of alkyl phenols in the mixture, and wherein the amount of solvent added with the water is from .5 to 10 parts of solvent per part of the mixture.

DANIEL B. LUTEN, JR. ALDO DE BENEDICTIS. 

